This invention relates generally to electronically controlled fuel injection systems and, more particularly, to a method and apparatus for delivering and controlling the fuel quantity of multiple fuel injections to the cylinder of an internal combustion engine during a fuel injection event based upon engine operating conditions.
Electronically controlled fuel injectors are well known in the art including both hydraulically actuated electronically controlled fuel injectors as well as mechanically actuated electronically controlled fuel injectors. Electronically controlled fuel injectors typically inject fuel into a specific engine cylinder as a function of an injection signal received from an electronic controller. These signals include waveforms that are indicative of a desired injection rate as well as the desired timing and quantity of fuel to be injected into the cylinders.
Emission regulations pertaining to engine exhaust emissions are increasingly becoming more restrictive throughout the world including, for example, restrictions on the emission of hydrocarbons, carbon monoxide, the release of particulate, and the release of nitrogen oxides (NOx). Tailoring the number of injections and the injection rate of fuel to a combustion chamber, as well as the desired quantity and timing of such fuel injections, is one way in which to control emissions and meet such emission standards. As a result, split fuel injection techniques have been utilized to modify the burn characteristics of the combustion process in an attempt to reduce emission and noise levels. Split injection typically involves splitting the total fuel delivery to the cylinder during a particular injection event into two separate fuel injections, for example, a pilot injection shot and a main injection shot. At different engine operating conditions, it may be necessary to use different injection strategies in order to achieve both desired engine operation and emissions control. For example, one split injection technique may be utilized at engine operating conditions including low engine speed and low engine load while other techniques may be utilized at different engine operating conditions. In the past, the controllability of split injection has been somewhat restricted by mechanical and other limitations associated with the particular types of injectors utilized. Even with more advanced electronically controlled injectors, during certain engine operating conditions, it is sometimes difficult to accurately control fuel delivery, even when utilizing current control signals.
As used throughout this disclosure, an injection event is defined as the injections that occur in a cylinder during one cycle of the engine. For example, one cycle of a four cycle engine for a particular cylinder, includes an intake, compression, expansion, and exhaust stroke. Therefore, the injection event in a four stroke engine includes the number of injections, or shots, that occur in a cylinder during the four strokes of the piston. The term shot as used in the art may also refer to the actual fuel injection or to the command current signal to a fuel injector or other fuel actuation device indicative of an injection or delivery of fuel to the engine.
Desired engine performance is not always achieved using split fuel injections at all engine speeds and engine load conditions. Based upon operating conditions, the injection timing, injection pressure, and quantity of fuel are desirably optimized in order to achieve desired emissions and desired fuel consumption. This is not always achieved in a split injection system due to a variety of reasons, including limitations on the different types of achievable injection waveform types, the amount of fuel injected during the separate fuel injections, when the injections take place during the particular injection event, the timing sequence between the injections, and how closely spaced injections influence each other. As a result, problems such as injecting fuel too rapidly within a given injection event and/or allowing fuel to be injected beyond a desired stopping point can adversely affect emission outputs and fuel economy.
In a system in which multiple injections and different injection waveforms are achievable, it is desirable to control and deliver any number of separate fuel injections to a particular cylinder so as to minimize emissions and fuel consumption based upon the operating conditions of the engine at that particular point in time, e.g. changes in speed, load, or ambient conditions. This may include splitting the fuel injection into more than two separate fuel shots during a particular injection event, providing larger fuel quantities in the pilot shot, advancing the pilot shot during the injection event, and adjusting the timing between the various multiple fuel injection shots in order to achieve desired emissions and desired fuel consumption. In some situations, it is also desirable to rate shape the front end of the fuel delivery to the cylinder to control the burn characteristics of the particular fuel being utilized. Further, in some situations the shot duration or the fuel quantity may be so small that it is not practical to inject the shot.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention, there is disclosed an electronically controlled fuel injection system which is capable of delivering multiple separate fuel injections to a particular cylinder of an internal combustion engine during a single injection event. The system includes at least one fuel injection device operable to deliver a plurality of fuel injection shots and a controller which is operable to determine the number of fuel shots, and the actual fuel amounts to be used in each shot.
In a preferred embodiment, the controller is operable to determine desired and minimum pilot shot fuel amounts, a minimum main shot fuel amount, and minimum and desired anchor shot fuel amounts. The total fuel quantity determined by the governor system is compared with various sums of these desired and minimum fuel amounts to determine the actual pilot, main, and anchor shot fuel amounts for injection by at least one fuel injection device. In proportioning the fuel among the multiple shots, the controller, in one embodiment, gives first priority to the main shot and second priority to the pilot shot. Thus, in one embodiment, if there is only enough fuel for the main shot, the pilot shot and anchor shot are set to substantially zero, and if there is only enough fuel for the main and pilot shots, the anchor shot is set to zero. If, however, there is not enough total fuel for the pilot and main shot, but there is enough fuel for the main and anchor shots, then the pilot shot will be set to substantially zero and the total fuel will be divided between the main shot and the anchor shot in accordance with the present invention.
In another aspect of the present invention, a computer readable medium contains instructions for controlling the fuel injection control system to partition the governor fuel output, the actual pilot, main, and anchor shot fuel amounts. The instructions determine if there is enough fuel output for the minimum main shot fuel amount, if there is enough governor fuel output for the desired pilot shot fuel amount, and if there is enough governor fuel output for the desired anchor shot fuel amount. Based on these various determinations, the instructions determine the actual pilot, main, and anchor shot fuel amounts.
In a preferred embodiment, a minimum pilot shot fuel amount and a minimum anchor shot fuel amount are also determined. To give the pilot shot priority over the anchor shot, the instructions determine if there is enough fuel for the pilot shot prior to determining if there is enough fuel for the anchor shot.
In another aspect of the present invention, a method is described for controlling a fuel injection control system to partition the governor fuel output. The method comprises determining the desired pilot and anchor shot fuel amounts and the minimum main shot fuel amount. The method then determines whether there is enough fuel for the minimum main shot fuel amount, the desired pilot shot fuel amount, and the desired anchor shot fuel amount. Based upon those determinations, the method then determines the actual pilot, main, and anchor shot fuel amounts.
In a preferred embodiment, the actual pilot shot fuel amount is injected prior to the actual main shot fuel amount, and the actual anchor shot fuel amount is injected after the actual main shot fuel amount. To determine the actual fuel amounts to be injected, the governor fuel output or total fuel quantity to be delivered is compared with various sums of the desired and minimum pilot shot fuel amounts, the minimum main shot fuel amount, and the minimum and desired anchor shot fuel amounts.